I have opened my tach and speedometer because of a powder being on the inside of the glass. The powder proved to be the reflective paint on the inside of the housing which casts an indirect light on the face. I thought it might be of use to the less intrepid/foolish who do not open the works to see what was inside. In particular note that the light bulbs insert into a tube which approaches but does not connect to the lens. The final connection is made by a short length of white, rubber, tube which fits into the socket tube and over the lens back. I found one intact, petrified tube on the ignition lens, and one perished, broken tube on the high-beam lens. The ignition lens was completely covered on the inside so no light could get through. I wonder how much cursing of the electrics might have ensued when the light stubbornly refused to work after I had replaced the entire harness?